1. Field of the Invention
The present invention relates to an X-ray apparatus, and a rotating anode X-ray tube applied to an X-ray apparatus.
2. Description of the Related Art
An X-ray apparatus using a rotary anode X-ray tube is composed of a rotary anode X-ray tube main body which contains a rotatably supported anode target in a vacuum enclosure, a stator coil which supplies a driving magnetic field from the outside of the X-ray tube main body to a rotor connected to the anode target, and a housing which contains the X-ray tube main body and stator coil.
The space between the housing and rotary anode X-ray tube main body is filled with a cooling medium to radiate the heat generated from the anode target, for example, insulating oil and non-oil/fat cooling liquid including water as a main component. Namely, the heat from the anode target is radiated to the cooling medium, and the cooling medium is cooled by convection, and the heat is exhausted. As a result, a heating element such as an anode target is cooled. An example of using an external heat exchanger for forced cooling, as well as circulating an insulating oil and a non-oil/fat cooling liquid, in order to ensure heat exhaustion, or a cooling efficiency (for example, PCT National Publication No. 2001-502473).
A large rotating anode X-ray tube apparatus having a large X-ray output uses a dynamic pressure plain bearing, in which a spiral groove is formed on the bearing surface of a rotary support mechanism to support an anode target rotatably, and the spiral groove is filled with liquid metal lubricant, such as gallium (Ga) and gallium-indium-tin (Ga—In—Sn) alloy.
To radiate the heat generated by an anode target in a rotating anode X-ray tube using a dynamic pressure plain bearing, there has been proposed a method of transmitting the generated heat from the anode target to a rotary body and further transmitting the heat to a fixed body through the bearing surface of the dynamic pressure plain bearing (for example, Jpn. Pat. Appln. KOKAI Publication No. 9-171789).
However, when a dynamic pressure plain bearing is used, a stator easily generates heat, and a temperature of the bearing may be rapidly increased in a short time.
When the temperature of the bearing is increased, the bearing metal surface and liquid metal lubricant react with each other, and a layer of intermetallic compound is generated. This layer increases in a short time, and may finally stop rotation.
Therefore, in a rotating anode X-ray tube apparatus using a liquid metal lubricant dynamic bearing, it is necessary to keep a sufficient cooling efficiency to prevent deterioration of life by the heating.